Archive for April, 2011

Reuters recently published an article reporting that only 10% of juvenile Chinstrap and Adélie penguins managed to survive their first journey back to the breeding colonies. The researchers had concluded that this was due to the effect of warming seas reducing the area of the available ice floes on which the ‘ice algae’ grow (algae growing over the bottoms of floating sea ice); and on which the krill population are said to feed. However, moulting abnormalities have also been noted in young penguins (New Scientist 16/4/2011 see below); and this effect was first noticed in captive penguins in South Africa – one could presume that they were not short of food, but were almost certainly fed the same food as their free-born relatives fishing for themselves. This set me thinking of the other possible reasons for the declining numbers of juvenile Chinstrap and Adélie penguins in Antarctic waters.

Some Adélie (Pygoscelis adeliae) Facts:

Adélie penguins stand up to 30 inches (75cms) in height and weigh in at a max. of 5.8kg; these are the penguins with the white circle around each eye. They arrive at their stony breeding grounds in October/November, and lay one egg which they take turns to incubate; the off-duty parent going out to sea to feed for up to 12 days at a time. Hatching and fledging completed, they leave with their young in February/March when the chicks are 50 – 60 days old, and spend the rest of the year out on the ice floes. Some have been found to travel as much as 17,600km over the winter period, and can reach speeds of 45mph in the water! So they do need a diet that is rich in fat and/or oils. Their populations have dropped by 65% over the past 25 years.

Some Chinstrap (Pygoscelis antarcticus) Facts:

Chinstrap penguins stand up to 27 inches (68cms) in height and weigh in at a max. of 6kg, although their weight is known to drop to 3kg; their defining characteristic is a thin line of black feathers forming a visual strap from the black back of their head right around their chins. They prefer stony ground for nesting but will nest on glaciers providing that they can find a few stones for the nest. Unlike the Adélie penguins, they lay two eggs and the off duty parent only stays away feeding for 6 days at a time. Apart from this the two species are very similar in their habits, leaving for their winter travels when the chicks are about 60 days old.

Perhaps strangely, I would have suspected that a build up of man-made chemicals (pollutants) are the main culprits for decrease in penguin numbers, rather than marine warming per se. However, as the oceans absorb more carbon dioxide, another mechanism comes into play. It maybe that there is a decrease in krill due to increases in the latter. This would have a knock on effect on the fish population as well as the penguins.

Increased concentrations of these chemicals e.g. DDT (banned in 1972) and PCBs, would affect all levels of the marine food chain and though some authors state that PCBs are not accumulative, I find this hard to believe. We already know that PCBs have reached the fat deposits of polar bears, seals and even the milk of Inuit women. We also know that PCBs are insoluble in water, but soluble in fat; therefore it would be strange if they did not accumulate in species at the top of the food chain. Their levels in fat tissues of mammals have been stated as being in the range of 10 – 0.1μg/gram (Tatsukawa, 1976). Another study done in the relatively warm Irish Sea by Holdgate (1979) showed levels of <10 – 30μg/kg wet weight in Zooplankton and gave a comparison of the levels found in dead and healthy guillemots. Those that died had 10,000 – 200,000μg/kg in their livers and 1,000 – 10,000μg/kg in the rest of their bodies. The healthy guillemots by comparison had 0 – 2,000μg in their livers and 1,000 – 7,000μg/kg in the rest of their bodies. I G Simmons, in The Ecology of Natural Resources (1981) noted that:

“In birds, PCBs can affect the metabolic rate and the structure and waterproofing of feathers”.

Obviously this would seriously affect the survival rate of penguins moving from their summer to winter quarters, during which time they are actively trying to build up fat supplies. Worryingly, the New Scientist magazine of 16 April 2011 reports on an article in Waterbirds, DOI: 10.1675/063.033.0321. This states that “some young penguins in South Africa and Argentina are not immediately replacing their ‘coats’ after moulting, thus leaving them bald for a time. The study’s authors think it is probably down to an infection but they have not yet found evidence of a parasite”. This abnormal moulting behaviour would definitely not favour survival, and could certainly be caused by high levels of PCBs in the body tissues of the young penguins. A reduction in metabolic rate would greatly exacerbate the problem in conditions of bad weather or lack of suitable food species.

It is interesting to note that most of the studies, relating to PCBs in the marine environment, have been carried out in polar seas. The following, relating to the Guillemot study, perhaps identifies the reason why fat soluble pollutants are so devastating in the Polar Regions:

“it is hypothesized that the guillemots which were the main victims, were caught at a time of storms and so metabolized PCBs in their fat as well as any which were ingested from their food, leading to the very high levels in their livers”.

Storms are a frequent occurrence in the Antarctic Ocean, so it would not be surprising to find that the penguins were affected in the same way as the guillemots.

The second process that may be affecting the krill populations, concerns higher levels of carbon dioxide in the atmosphere; and these will inevitably lead to higher concentrations in the planet’s water bodies. In the oceans this reacts with carbonates to form bicarbonates; an action that causes the water to become more acidic and at the same time removes a form of calcium carbonate known as aragonite from the water body. This is used by molluscs and crustaceans (krill) to form their shells/skeletons and has come to the notice of marine biologists in the context of a potential hazard to our coral reefs, where the concentration of aragonite in the water is critical to the growth of the reef. According to Bronte Tilbrook (CSIRO, Hobart, Tasmania, Australia) in the New Scientist of 16th April 2011, at an aragonite saturation level of 4.5 the coral grows well, but in areas where the level drops to 2.8, then the coral starts to dissolve. Even if less likely in the cold waters of the Antarctic ocean, this reaction could still take place, and if it did would certainly affect the survival and growth of the krill population. Oxygen levels too, are important; and lower levels in the atmosphere, due to combustion of fossil fuels, could cause a reduction of the amount of oxygen dissolving in the water. This too could have a very damaging effect on both algae and krill, as well as being an extra cause of stress to the fish population. So the water levels of both carbon dioxide and oxygen could have a knock-on effect on the survival of the penguins; though it is highly unlikely that either is involved with the duration of the moulting process in these penguins.

I am also surprised to find that the researchers consider that penguins, even the Adélie and Chinstrap, are dependent on the krill which are dependent on marine algae. Although Adélie penguins currently seem to feed mainly on krill; before the early 1800s, when there were large populations of Antarctic Fur Seals and Baleen whales competing for the krill in Antarctic waters, they ate mostly fish and squid. This was deduced following studies of preserved egg shells at the penguin rookeries. Therefore, it seems unlikely that if the krill population were to drop, the penguins would not simply return to their old basic and eat more fish and small squid. However, fish and squid do feed widely on krill (small shrimps and shrimp-like crustacea that are approx. 7% fat and 16% protein) and the krill do feed on the algae, so there could be a knock-on effect if the abundance of algae fell. But many of the algae in these waters are said to be single celled organisms drifting free in the water column. It is these and the smaller zoo-plankton that are the main food source for the krill in the diets of both fish and whales’. Krill numbers would also be affected by the passive uptake of pollutants from the water as they feed, thus affecting the health and survival of their predators further up the food chain.

It is also worth noting that, since we humans have decimated the Baleen whale and Antarctic Fur Seal populations that fed on the krill in large quantities, we have decided that the excess krill might be harvested for human use. It was said that the productivity of the krill was >50 million t/yr in Antarctic seas and this yield of biomass has been exploited by us in recent decades. If indeed the penguins’ problems are related to the uptake of pollutants in their food, as hypothesised; one would expect to see some effects with similar problems in the presently recovering Antarctic Fur Seal population. However, if fish form the greater part of their diet, and pollutants such as PCBs have only reached critical concentrations in krill and small squid, then the seals may be safe for the present.

So in conclusion it would be interesting to know whether Deborah Zabarenko (author of the Reuter’s article) or the Lenfest Ocean Program have measured the PCB concentrations in the livers of any members of the penguin population. NB the article above does not seem to mention: the finding of any corpses; nor quantitative studies on the populations of free or attached Antarctic algae; nor pollutant concentrations in krill. Therefore, the conclusions may need some considerable further work before they could be described as an effect that was definitely due to polar ocean warming. However, it is certainly true that marine warming would result in a harmful stress to this prolific ecosystem; and this could in turn lead to impairment of the metabolic and immune systems of species living in these waters, making them even more susceptible to pollutants. There is also a need to check for an increase in the acidity of polar seas, in order to be able to rule out the carbon dioxide effect.